The field of the present invention relates to reading and writing audio/visual data to and from hard disc drives. More particularly the present invention relates to methods and apparatus for improving performance when accessing audio/visual data stored on an disc drive.
In general, there are two types of data stored on disc drives, normal computer data and audio/visual data. Audio/visual data relates to computer readable information stored on disc drives wherein the data corresponds to information that produces audio signals and/or visual signals. These audio and visual signals arc used by a computer host to translate them into audio and video presentations through either a speaker or a monitor. Audio and visual data typically involves relatively large amounts of information that must be stored on a computer disc drive in order to produce actual audio or actual video. As an example, a movie that is approximately two hours in length may require approximately four gigabytes of computer storage space.
In addition to consuming considerable computer storage space, the information must also be transferred from the storage space to a host computer at a significantly high rate of speed. The host computer processes the information and conducts the information to an output terminal connected to either the speaker or monitor. As an example, a host computer system may comprise a xe2x80x9cset top boxxe2x80x9d which receives television signals from either a cable connection or some other communications conductor. The set top box manages these television signals to ultimately provide signals to a connected television.
Often, the incoming signals are received in a particular format, such as Moving Picture Experts Group (MPEG) standards format or some variation thereof. The MPEG standards are an evolving set of standards for video and audio compression. As an example, MPEG-1 was designed for coding progressive video at a transmission rate of about 1.5 million bits per second. MPEG-2 was designed for coding interlaced images at transmission rates above 4 million bits per second. MPEG-2 is used for digital TV broadcast and DVD. The set top box must decompress or otherwise manipulate the data to present it to the television for viewing. Also, the set top box has memory so that the viewer is able to pause the viewing process, causing the incoming information to be stored in memory, and pick up where the viewer left off at a later time. Thus, upon re-starting the viewing process, the user views recorded information. In this particular situation, the set top box must manage two television signals or data streams, the incoming signal to record to memory and the outgoing signal conducted from memory to the user interface.
With the advent of picture-in-picture viewing, the set top box may be requested to provide two, and potentially more, separate data streams to the user interface. Of course, as more and more signals are conducted to the television, the set top box must handle significantly more information. In the situation where the user is viewing two signals and momentarily pauses each signal, upon resuming, the set top box must handle four data streams, two incoming signals and two outgoing signals. Consequently, the information must be handled efficiently in order to avoid losing incoming information or causing undesirable pauses in presentation of the information to the user. Additionally, if the information is stored to a disc drive, the information must be read from the disc at a relatively high rate in order to allow the host computer to process the information and present it to the user or viewer in real time, i.e., at a speed related to which the movie was recorded. Often, the information is not read quickly enough causing the resulting audio/visual presentation to contain gaps or otherwise have a decreased performance.
Typical Advanced Technology Attachment (xe2x80x9cATAxe2x80x9d) disc drives may be used to store the audio/visual information managed by the set top box. Unfortunately however, the typical ATA drive is not designed specifically for audio/visual data, and is in fact designed to work with normal computer data. Since normal computer data differs from audio/visual data in that each bit of normal computer data is potentially critical to the operational flow of the computer process, the typical ATA drive is designed to perform several tests on the data as it is stored and retrieved in order to insure that the correct information is stored and retrieved. The normal computer data is considered to be xe2x80x9creliability criticalxe2x80x9d wherein correct data storage and retrieval is much more important than any loss in time associated with achieving such reliability.
Audio/visual data, on the other hand is considered to be time or performance critical. If some of the audio/visual data is corrupt and unreadable, typically the presentation to the user is not seriously affected. Often such a loss in data may present only a flicker in the audio or video signal to the user or otherwise be undetectable. However, if the information is presented with many pauses or skips due to losses in time associated with trying to insure data reliability, the resulting presentation to the user is unsatisfactory.
One specific problem associated with some set top boxes and their ability to manage many streams of data using ATA disc drives is that the set top box incurs a significant amount of overhead time loss between requests for data from the ATA disc drive. In essence, each request decreases the performance of the audio/visual data manipulation process.
Another specific problem relates to dropping a revolution during communication since the data is sequentially placed on the disc drive.
The present invention relates to a disc drive system and process which manages the reading and writing of audio/visual data to and from the storage medium of the disc drive. With respect to one aspect of the present invention, the disc drive achieves improved performance by reading and writing the audio/visual data in relatively large blocks of data during one command. Instead of accessing less than a track during one command as prior art disc drives, the present invention allows for ten or more tracks of data to be accessed during one data access command. Increasing the accessed block size decreases lost seek time and other overhead time that occurs each time a command is requested to conducted to the drive.
In accordance with another aspect of the present invention, improved audio/visual data access performance is achieved by limiting the number of retries or error correction processes that occur during normal read and write data accesses. Reducing or limiting the number of retries significantly increases the throughput of audio/visual data and the erroneous data is typically not critical to the operation or presentation of the audio/visual signal.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.